The overall aim of this proposal is to demonstrate the physiologic function of factor XII (XII) and prolylcarboxypeptidase (PRCP) on angiogenesis, vascular signaling pathways, arterial thrombosis risk, or hypertension. The overall hypothesis of this proposal is that factor XII and prolycarboxypeptidase modulate vascular function and arterial thrombosis risk in vivo. Preliminary studies indicate that factor XII (XII) has an outside-in signaling pathway mediated by uPAR that is blocked by high molecular weight kininogen (HK) that leads to cell proliferation, growth, and angiogenesis. Furthermore, prolylcarboxypeptidase (PRCP), an endothelial cell plasma prekallikrein activator, influences constitutive arterial thrombosis risk and blood pressure in vivo. PRCP murine hypomorphs are lean, prothrombotic and hypertensive. Our data indicate that XII regulates angiogenesis through an outside-in signaling pathways and that reduced prolylcarboxypeptidase in a murine hypomorphs increases arterial thrombosis risk associated with hypertension in the intravascular compartment. The specific aims of this proposal follow: Specific Aim 1: The outside-in signaling mechanism(s) of XII through uPAR and the EGFR on endothelial cells will be elucidated to characterize its pathway(s) leading to angiogenesis. The hypothesis of this specific aim is that XII stimulates endothelial cell signaling, growth and angiogenesis to promote vascular growth after injury. This specific aim will examine the following questions: 1) Characterize angiogenesis defects in XII KO mice and determine XII's contribution to the repair mechanisms after vascular injury. 2) Determine the mechanism(s) by which XII interacts with the EGFR on endothelial cells and determine this pathway's influence on angiogenesis and injury repair processes. Specific Aim 2: The mechanism(s) by which PRCP contributes to reduced thrombosis risk and blood pressure in vivo will be characterized. The hypothesis of this specific aim is that PRCP reduces arterial thrombosis risk and lowers blood pressure by reducing tissue reactive oxygen species. This specific aim will examine the following questions: 1) Determine the mechanism(s) by which reduced PRCP in murine hypomorphs results in increased reactive oxygen species and eNOS uncoupling leading to its prothrombotic and hypertensive state. 2) Determine if the mechanism(s) for hypertension and thrombosis risk in the PRCP murine hypomorphs are linked. 3) Determine if reduced PRCP metabolism of a-melanocyte stimulating hormone contributes to PRCP murine hypomorphs' prothrombotic and hypertensive phenotype. The specific aims of this proposal are derived from observations on how XII influences endothelial cell signaling, growth, and angiogenesis and the phenotypes of the newly created PRCP murine hypomorph. The XII signaling pathway leads to in vitro and in vivo angiogenesis. PRCP modulates arterial thrombosis risk and blood pressure. The PRCP murine hypomorphs have shortened times to arterial thrombosis and are constitutively hypertensive. New evidence indicates increased reactive oxygen species and peroxynitrite and uncoupled eNOS in their arterial vessels. The increased arterial thrombosis risk is corrected with treatment with the antioxidant Tempol. In vitro and in vivo investigations on XII and PRCP may indicate new therapeutic targets to modulate arterial thrombosis and hypertension without increasing bleeding risk.